C version, bash cleanup.

day15/ex1-c.c

@@ -0,0 +1,40 @@
+/* ex1-c: Advent2020 game, day 15/games 1 and 2
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(ac, av)
+    int ac;
+    char **av;
+{
+    char line[1024], *pval;
+    int target, cur=0, *array;
+    register int diff, previous=-1;
+
+    if (ac != 2) {
+        fprintf(stderr, "usage: %s number\n", *av);
+    }
+    target=atol(*(av+1));
+    array=malloc(sizeof(unsigned long) * target);
+    for (int i=0; i<target; ++i) {
+        array[i]=-1;
+    }
+
+    fgets(line, sizeof line, stdin);
+    pval=strtok(line, ",");
+    do {
+        diff=atoi(pval);
+        array[diff]=cur++;
+    } while (pval=strtok(NULL, ","));
+
+    for (; cur<target; ++cur) {
+        diff = (previous>=0)? cur-previous-1: 0;
+        previous=array[diff];
+        array[diff]=cur;
+    }
+
+    printf("%s : res[%d]=%d\n", *av, target, diff);
+    exit (0);
+}